1. Technical Field
The present invention relates to light-emitting devices.
2. Related Art
Light-emitting devices that include light-emitting elements, such as organic electroluminescent (EL) elements, on substrates are now widely used as, for example, displays and exposure units of electrophotographic image-forming apparatuses.
Such light-emitting devices require enough durability to withstand an extended period of light emission. One factor that degrades the light-emission characteristics of organic EL elements is dark spots. A dark spot occurs in a laminate of a transparent electrode, a light-emitting layer (organic layer), and a back electrode if the organic layer is delaminated from the back electrode by the intrusion of water deposited on components of the organic EL elements or water (moisture) or atmospheric gas, including oxygen, entering the organic EL elements into the laminate through, for example, defects in the surface of the back electrode.
To increase the reliability and life of the organic EL elements in the light-emitting devices, it is important to make sure that the light-emitting layer and the electrodes of the organic EL elements are insulated from the atmospheric gas. To that end, there are some known techniques for bonding a sealing member with an adhesive to a substrate (transparent substrate) on which organic EL elements are formed to seal the organic EL elements therebetween, thereby protecting the organic EL elements from, for example, atmospheric gas.
JP-A-2002-280168, for example, discloses a light-emitting device including a transparent glass substrate, a laminate on the substrate, a glass sealing member having a recess and hermetically bonded to the substrate with an adhesive so as to cover the laminate, and a moisture adsorber on the surface of the sealing member opposite the laminate. The laminate includes a transparent electrode (anode) formed of, for example, indium tin oxide (ITO), an organic layer at least including a light-emitting layer, and a nontransparent back electrode (cathode) formed of, for example, aluminum (Al). The moisture adsorber is formed of a compound that chemically adsorbs water and that remains solid after adsorbing water.
For such hollow sealing with an adhesive and a glass lid, however, the atmospheric gas may intrude into the internal space through the interface between the sealing member and the substrate because of insufficient adhesion, depending on the thickness and width, for example, of the adhesive applied.